San Francisco public health officials have received their first major batch of swine flu vaccine and are planning to offer it to people most vulnerable to the influenza strain at 10 sites starting Thursday.

City officials received 28,000 doses of the injectable vaccine, Mayor Gavin Newsom said Monday, and more are on the way.

"We expect a lot more doses over the course of the next few weeks," Newsom said. "We're confident that we'll be able to meet the demand."

The vaccine has been trickling into the Bay Area. Kaiser Permanente, the largest health care provider in San Francisco and the region, has had a limited supply of the vaccine.

Public health officials are directing anyone who has a physician to contact their doctor about getting vaccinated for H1N1, a form of influenza.

Those who don't have a doctor and are most at risk from the swine flu can get the vaccine for free at nine of the 10 public health clinics starting Thursday. That group includes pregnant women, youths ranging from 6 months to 24 years, caregivers for infants younger than 6 months old and adults with weakened immune systems.

Public health officials are urging only those at risk to get the vaccine at first, said Dr. Mitch Katz, director of public health.

Swine flu has killed more than 1,000 people in the United States since April, according to the latest estimate from the Centers for Disease Control and Prevention, and infectious disease experts believe it has infected millions worldwide.

Newsom urged a sense of perspective.

"In many ways, this is a more mild flu than the traditional seasonal influenza," said Newsom, who got vaccinated late last week. "I hope we avoid a large rush down to all the clinics."

H1N1 vaccine

The San Francisco Department of Public Health will be providing the H1N1 flu vaccine free to high-risk people for three days starting Thursday at these sites: